The invention concerns an extraction valve for an overpressurized gas from a compressed gas reservoir.
Extraction valves for overpressurized gases from a compressed gas reservoir, in particular for compressed natural gas or compressed hydrogen, are known from the general state of the art. Typically, the rated pressures are in the order of magnitude of around 26 MPa for natural gas, in the order of magnitude of 70 MPa for hydrogen. Typically, the construction of such extraction valves is in the form of so-called pilot valves in which the pressure of the gas is applied via a pilot bore or a control bore, in a pressure sleeve presenting additional actuating elements of the extraction valve, as an auxiliary for opening or closing an extraction piston controlling an extraction cross-section. The extraction piston should hence be typically actuated directly or indirectly via an electromagnetic coil and is operated by the pressure building up in the pressure sleeve via the pilot bore. An exemplary extraction valve in the form of a pilot valve is described in particular in EP 1 682 801 B1.
The core, when developing such pilot valves, lies typically in the actuation system of the extraction piston via the already mentioned, mostly electromagnetic triggering and the configuration of the extraction piston and of the pilot bore. The EP document remains silent to a vast extent as regards the extraction opening properly speaking, which is designated as a valve main seat. Different requirements should still be met in this field. Good sealing, in particular when using such extraction valves in compressed gas reservoirs for hydrogen, is essential as well as high durability on the other hand so that the assembly can sustain a large number of operating cycles.
An electromagnetic extraction valve is known from US 2014/0166915 A1. To ensure good sealing between the valve body and the valve seat, a groove containing an elastic gasket is provided in the conical valve body. The assembly is critical in particular for sealing against hydrogen since high cycle stability is difficult to achieve on the one hand as well as good seal property against hydrogen on the other hand using the mentioned materials. Another similar assembly is also disclosed in US 2003/0151018 A1. The main difference lies in that in the assembly described, the sealing material is not provided in the region of the valve body but of the valve seat. The valve body properly speaking is designed as a semi-circular element so as to provide the best possible fit, ideally a linear circumferential contact line between the valve seat and the valve body. Here as well, as with hydrogen generally, good sealing effect is quite difficult to achieve. In particular in the presence of strong temperature fluctuations, as can be encountered in vehicles, the highest requirements should be set to the materials as regards their elasticity on the one hand and as regards the elasticity across a very large field of application temperatures on the other hand.
For that reason and as it is known and usual from the general state of the art, with an assembly, which seems for example comparable to the assembly shown in the last-mentioned US document, sealing elements inside the valve seat or valve body can be omitted altogether. With such assemblies, the whole valve body and/or valve seat can be made of a single material, in particular a metallic material. Such assemblies can achieve comparatively good tightness, in particular in use in compressed gas reservoirs for hydrogen. The inventor is fully aware that the assembly is highly critical in terms of wear or damage, in particular in the region of the valve seat. Since gas, for example hydrogen, is present with a rated pressure of 70 MPa on one side of a sealing edge formed between the valve seat and the valve body and after opening the extraction valve by moving the extraction piston suddenly, the gas is relaxed to a much lower pressure, for example of 20-40 MPa, the stress on the material in the region of the valve seat then becomes enormous. According to the inventor's experience, the region of the valve seat becomes extremely damaged typically after a few thousand switching cycles of the extraction piston. We assume here that the frequent sudden change in pressure ratios on the one hand and the overflow of this region with very high flow velocity immediately after opening the extraction piston on the other hand are responsible.
Another aspect is that gases in the compressed gas reservoir may often contain minimal quantities of very small abrasive particles which can lead to a kind of wear of the valve seat in cooperation with the high volume flows and velocities in the region of the valve seat. All in all, there is the danger with the assemblies known so far of insufficient tightness on the one hand and of premature damage of the valve seat due to the great number of cycles as can be the case with a pilot valve in particular, on the other hand.
It is an object of the present invention is to provide an extraction valve which is designed to ensure safe and reliable extraction of the gas stored under overpressure over a long usage time period of the extraction valve.
With the extraction valve according to the invention, the inflow chamber through which the overpressurized gas from the compressed gas reservoir flows into the extraction valve is formed totally or partially circumferentially with respect to central axis of the extraction piston. There is no direct connection to the region of the valve seat, as well with the assemblies according to the state of the art as with the extraction valve according to the invention. Far more, it is connected in the axial direction of the extraction piston against a flow direction of the gas when the extraction piston is in open position, between the valve seat and the valve body via an intermediate connection with an intermediate volume. The intermediate volume properly speaking includes a connection with the region in which the valve seat and the valve body co-operate. The overpressurized gas flowing into the extraction valve is also diverted from the inflow chamber into the opposite direction of the extraction flow downstream and reaches into the intermediate volume situated there. The intermediate volume is then connected to the region of the valve seat and the valve body so that gas is discharged between the valve seat and the valve body, from the intermediate volume through the extraction opening, when the valve is opened. The assembly thus enables incoming flow to the valve seat essentially in axial direction of the extraction valve or in axial direction parallel to the axis of the extraction piston. To do so, the mechanical stress of the valve seat is reduced significantly so that the lifetime of the valve seat can be increased, even with a large number of strokes of the extraction piston.
According to a particular advantageous further embodiment of the idea, it is also provided that the connection is formed as a central opening around the extraction piston. The intermediate volume there includes a central opening according to this advantageous further development of the extraction valve according to the invention into which gas flows accordingly so as to flow along the extraction piston in axial direction between the valve body of the extraction piston and the valve seat.
A further very advantageous embodiment of the idea moreover sets forth that the intermediate connection is designed as an annular intermediate element via several bores. Such an annular intermediate element can be mounted between the inflow chamber on the one hand and the intermediate volume on the other hand. The intermediate element is thus annular since the extraction piston runs centrally through the intermediate element. Several bores are distributed over the circumference, extending in axial direction, in the material of the annular intermediate element. Gas flows from the inflow chamber into the intermediate volume through the bores. Gas can then spread itself uniformly in the intermediate volume and flows from there ideally through the central opening of the annular intermediate element, through which the extraction piston runs, along the latter in direction of the valve seat.
In a further very favorable embodiment of the extraction valve according to the invention it is provided that the valve seat carrier is retained in the axial direction via the intermediate element. The valve seat carrier can also be retained in axial direction by the intermediate element so that a very compact assembly can be achieved, in which the annular intermediate element fulfils the functionality of the intermediate connection through the bores in axial direction against the flow direction during extraction on the one hand and the mechanical fastening of the valve seat carrier on the other hand.
The intermediate element is in a very favorable further development of the idea engaged tightly with the region of the valve seat carrier surrounding the valve seat, for which purpose the intermediate element includes a sealing edge protruding in particular in the direction of the valve seat carrier. The sealing engagement between the intermediate element and the valve seat carrier prevents the pressurized gas from flowing through possible gaps directly from the inflow chamber into the region of the valve seat. The sealing engagement can in particular be realised in such a way that a protruding sealing edge, a so-called biting edge is provided at the intermediate element, which edge is deformed when pressing the intermediate element against the valve seat carrier and/or penetrates into the material of the valve seat carrier so as to generate a reliable sealing effect.
The valve body and/or the valve seat can hence be designed as a spherical component on the one hand and as a spherical cap on the other hand. The combination between a spherical component and a conical valve seat can also be envisaged. A particular good sealing effect can be achieved when, according to a very favorable embodiment of the idea, the portion of the extraction piston used as a valve body is conical and the conical valve body co-operates with a conical valve seat whereas the opening angle of the cones of the valve body and of the valve seat depart from each other. Such a conical valve body can then co-operate ideally with the conical valve seat. Conical in the sense of the present invention should be understood as a form which can also designated as the envelope surface of a truncated cone. To do so, the term conical also encompasses in the context of the invention not only the envelope surface of a single truncated cone but also several successively connected envelope surfaces of different truncated cones with different opening angles. The truncated cone which provides the shape, can also have several axial sections of different opening angles. Such as truncated cone confers very good sealing effect, first of all if according to the idea, the conical valve body in the region of contact with the conical valve seat has a smaller or a larger opening angle of the truncated cone than the valve seat. The difference in the opening angles, departing from each other, of the truncated cones of both conical co-operating elements, valve body and valve seat, provides a substantially linear and circumferential contact of the valve body on the valve seat. The result is consequently high surface pressure which provides very good sealing effect, which proves extremely advantageous in case of hydrogen as regards the tightness of the extraction valve.
A further extraordinarily favorable embodiment of the extraction valve according to the invention can see to it that the portion of the valve seat co-operating with the valve body has a sealing lip protruding in axial direction of the intermediate volume. Such a sealing lip protruding in axial direction above the material of the valve seat carrier provides high elasticity of the valve seat in the region of the sealing lip. The result is good contact of the valve seat against the valve body and consequently a very good sealing effect.
Such a sealing lip has now the shortcoming, as shown in practice, of being comparatively sensitive. In particular the incoming flow of a large quantity of overpressurized gas as well as significant differential pressure along the sealing lip when opening the extraction valve can easily damage the sealing lip. Consequently, according to a further very favorable embodiment of the idea, it can be provided that the sealing lip lies, totally or at least partially, behind a protrusion as seen in direction of the inflowing gas during extraction. Such a protrusion can protect the sealing during the extraction cycle properly speaking of the overpressurized gas against direct incoming flow of the gas so that the protrusion shelters the sealing lip from the volume flow of the gas and therefore protects the lip mechanically. It can therefore be provided in a very advantageous further embodiment of this idea, that the protrusion is formed in the intermediate element. If the intermediate element is present according to embodiment variation of the invention described above, the protrusion can be formed ideally in the intermediate element. First of all if the intermediate element and the valve seat, which now includes the sealing lip, co-operate mechanically, for example because, as described above as a particularly advantageous further development, the intermediate element maintains the valve seat in axial direction, the assembly can provide for the protection of the sealing lip extraordinarily simply and efficiently, which increases the robustness and the lifetime of the extraction valve.
It can therefore be provided in a very advantageous further embodiment of this idea when using a sealing lip, that an activation volume is arranged around the sealing lip which is connected with the pressurized gas present at the valve body and the valve seat when the extraction piston is in closed position, in particular via a gap between the protrusion and the sealing lip. Such an activation volume on the side of the sealing lip facing away from the valve body, when the extraction piston is in closed position, results in that the comparatively elastic sealing lip is pressed in direction of the valve body due to the pressure exerted by the overpressurized gas in the region of the activation volume. The pressure of the overpressurized gas also contributes to pressing the sealing lip as firmly and hermetically against the valve body. The gas properly speaking also contributes to improving the sealing effect, hence the reason we are talking here of a pressure activation.
According to a very favorable further development of the embodiment, it can be moreover provided that the activation volume comprises a targeted connection with the region of the upcoming gas via at least one connection opening in the region of the sealing lip. Such a targeted connection, which can be formed for example as a bore through the sealing lip, as a spiral channel or as a radial groove through the sealing lip, provides very good inflow of the gas into the activation volume independently of the size of the gap between the protrusion and the sealing lip. This guarantees on the one hand reliable filling of the activation volume and hence reliable support of the sealing effect by the pressure activation. Moreover, when moving the extraction piston into the open position, it enables targeted discharge of the gas through the connection openings from the region of the activation volume. Since the comparatively sudden outflow can take place through the targeted connections safely and reliably in a predefined region and designed constructively to that effect, any possible impairments of the sealing lip caused by the outflow can be controlled much more easily than if the outflow would run along the gap over the whole region of the sealing lip or over any accidental region of the lip.
According to an additional very favorable embodiment of this idea, it can moreover be provided that a sealing material is arranged in the activation volume. A sealing material, for example a sealing ring, can be inserted extraordinarily simply and efficiently into the activation volume since the activation volume typically includes an annular chamber, situated from the central axis of the extraction valve outside the sealing lip. The sealing material has here no influence whatsoever on the sealing effect. It is advisable to reduce the volume of the activation volume only for that purpose. The remaining volume between the sealing material and the sealing lip only suffices to ensure the pressure activation described above. The inventor is fully aware that immediately after lifting the valve body from the valve seat for the first time, gas flows suddenly along the sealing lip in direction of the valve seat out of the region of the activation volume. He has observed that the flow causes an additional mechanical stress of the sealing lip, to the extent that the sealing lip is deformed. In the worst case, the sealing lip is then damaged and/or destroyed by the extraction piston or valve body during the next stroke. The improved flow according to the basic configuration of the extraction valve according to the invention, and in particular the activation volume through the sealing material, for example a very soft sealing ring, designed with a small useful filling of NBR of FKM, enable extended lifetime since on the one hand very uniform flow can be achieved and on the other hand pressure changes occurring suddenly due a comparatively sensitive sealing lip can be mitigated significantly by reducing the activation volume. A certain activation volume remains which provides an advantage in terms of sealing the extraction valve when the extraction piston is in closed position. It goes without saying that the sealing material must be suitable for the contemplated use, in particular the predefined pressure and temperature range. In particular, its glass transition temperature should be much smaller than 40° C. The sealing material should retain its elasticity over the whole temperature range. Moreover, the sealing material should be elastic and resistant against decompressive explosion.
The inflow chamber of the inlet valve according to the invention is arranged, as explained, totally or partially circumferentially around a central axis of the extraction piston and is not in fluid connection with the region of the valve seat, beyond the intermediate volume. The inflow chamber can be designed annular and in the shape of annular segments according to an advantageous further embodiment. It can hence be formed totally or partially circumferentially around the central axis of the extraction valve. According to an additional very favorable embodiment of this idea, it can moreover be provided that the inflow chamber is spiral-shaped. Such a spiral-shaped inflow chamber, in an embodiment as known for example from the inflow chamber with turbines, ensures uniform distribution of the outflowing gas through the bores in the intermediate element in direction of the intermediate volume. The result is that at the end of the day a uniform streamline-distribution of the gas in the intermediate volume and consequently uniform incident flow through the valve seat are improved so that its mechanical stress is distributed very evenly over the whole surface of the valve seat.
It can therefore be provided in a very advantageous further embodiment of this idea that the inflow chamber is connected to the volume in the compressed gas reservoir via a feed line emerging tangentially into the inflow chamber. In particular, such a tangential inflow of gas into the inflow chamber enables uniform distribution of gas in the whole inflow chamber. The danger of gas spreading into the intermediate volume and from there into the discharge opening situated in the center of the region of the valve seat, in a path preferably on the side of the inflow opening is avoided. The more uniform the flow of gas, the smaller the local stresses on the material of the valve seat and of the valve body, in particular of a sealing lip of the valve seat, in case such a sealing lip is present. Moreover, the result is a smaller pressure drop over the whole extraction path.
In a further very favorable embodiment of the extraction valve according to the invention it is moreover provided that the narrowest flowable cross-section for the gas flowing out, when the extraction piston is in open position, is arranged between the valve seat and the valve body in flow direction of the gas after the region of the valve seat, in which the seat co-operates with the valve body, when the extraction piston is in closed position. The narrowest flowable cross-section inside the extraction valve hence lies deliberately in the annular gap which is formed between the valve body and the valve seat when the extraction piston is in open position. The region of the narrowest flowable cross-section controls on the one hand the volume flow rate through the extraction valve. On the other hand, a major portion of the pressure drop and of the turbulent kinetic energy builds up between the inflow chamber on the one hand and the outflow chamber on the other hand. The materials situated in the region of the narrowest flowable cross-section are thus exposed to particularly high mechanical stress. Since the materials are then arranged in the flow direction after the region of the valve seat, which when the extraction piston is in closed position is in sealing engagement with the valve body, the region can be designed, in particular in the region of a tip of the extraction piston, which protrudes through the valve seat, in order to keep the mechanical stress away from the critical region of the valve body and valve seat.
In a further very favorable embodiment of the extraction valve according to the invention in the variation with the bores in the intermediate element, it can now be provided moreover that a guiding pin connected to the extraction piston meshes into one of the bores. First of all with a tangential inflow of gas into the inflow chamber, it can be at the end of the day the bore at which the surrounding gas arrives. The guiding pin which operates between the intermediate element and the extraction piston sees to it that the angular position of the extraction piston and hence the angular position of the valve body connected thereto remains unchanged in circumferential direction. The guiding pin also determines the angular position between the extraction piston (formed typically rotationally symmetric, with the exception of the guiding pin) and the valve seat accordingly. The fastening of the angular position enables the same regions of the valve body and of the valve seat always to co-operate. Since possible irregularities and manufacturing tolerances in the region of the valve body and of the valve seat can be corrected with increased use and the co-operation of the surfaces, the sealing effect can be improved at least after a certain useful life of the extraction valve, inasmuch as the minimal irregularities, which are unavoidable during manufacture, can compensate each other and thereby improve the sealing effect. If the extraction piston could rotate freely, different spots would always co-operate, which would deteriorate the sealing effect of the assembly.
In addition to this advantage when achieving very good sealing effect by preventing the rotation of the extraction piston by the guiding pin, the penetration of the guiding pin into one of the bores prevents the bore independently of the position of the extraction piston from being traversed by the gas, or only along a small gap between the wall of the bore and the guiding pin. One of the bores can also be prevented from conveying gas from the inflow chamber into the intermediate volume, to a vast extent. In particular, with a tangential inflow gas into the inflow chamber, gas is distributed around the whole periphery of the annular or spiral-shaped (for example) inflow chamber. In particular with an annular inflow chamber, it may happen in practice that a portion of the gas does not follow the tangential impulse but rather flows into the bore situated immediately close to the mouth of the inlet pipe. In practice, the flow could not be distributed uniformly over the individual bores. A portion of the gas would “branch off” against the desired flow direction and consequently disturb the flow of gas flowing uniformly into the intermediate volume, possibly with a slight turbulence. Since the guiding pin can now use the particularly critical bore, the constant angular position of the extraction piston with respect to the valve seat is ensured on the one hand regardless of the strokes of the extraction piston and on the other hand, the guiding pin, which penetrates into the bore at least partially in all positions of the extraction piston, blocks the particularly critical bore to a vast extent so that it cannot affect negatively the uniform flow distribution.
According to a particularly advantageous further embodiment of the extraction valve of the invention the valve seat carrier and/or the extraction piston can be formed of high performance plastic, in particular of high performance thermoplastic resin. The use of high performance plastic, such as for instance PEEK (poly ether ether ketone), PI (polyimide), PAI (polyamide imide) or another high performance plastic is particularly advantageous. The high performance plastics have a glass transition and melting temperature, which lie above the temperatures occurring usually in operation. The result is a regular and homogeneous material property in the whole temperature range in which the extraction valve is operated. Moreover, high performance plastics have a certain residual elasticity, of approx. 3%, with mechanical dimensional stability. This is sufficient to guarantee a good sealing installation between the valve seat and the valve body. Plastics can be machined quite well as required. The machining may consist for instance in injection stamping or sintering, in particular with a mechanical rectification in the region of the undercut of the sealing lip forming the activation volume. Moreover, they exhibit very good sliding properties, high resistance to abrasion and very good mechanical properties. They are therefore absolutely ideal to form the valve seat and/or the valve body according to the invention. In particular, the valve seat, if present, is formed as a single piece with the sealing lip, and enables a very simple and efficient assembly by using such high performance plastics. For instance, the valve seat can be manufactured with a sealing lip of PEEK or PI. In such a case, it would co-operate ideally with a valve seat mounted as a single-piece on the extraction piston which is made of the same material of the extraction piston, for example a steel material, such as in particular 1.4016IM, 1.4435 or SUSF316L or even of one of the high performance plastics mentioned.
As already mentioned, the extraction valve can be realised as a pilot valve, according to a particularly advantageous embodiment, whereas the assembly of the extraction valve according to the invention does not really require such as pilot valve. In particular, the described assembly of the extraction valve can also be integrated as an internal main gasket of a check valve situated in the refueling path, as used for instance in the filling path of a so-called On-Tank-Valve (OTV) or in a tank filling neck connected upstream. The assembly can also be used with a typically present second check valve, formed as a safety check valve.
The particular advantages of the extraction valve according to the invention come to the forefront in the case of a pilot valve, in particular if the pilot valve is formed for a hydrogen tank, for example an OTV on a hydrogen tank in the form of a compressed gas reservoir. The particularly good properties in terms of sealing effect on the one hand and in terms of very high cycle stability at high pressure gradients or differential pressures on the other hand present decisive advantages of the extraction valve according to the invention, which come to fruition in particular if it takes the form of a pilot valve for hydrogen tanks.
Further advantageous embodiments of the extraction valve according to the invention can be seen in the exemplary embodiments which are described more in detail below with reference to the Figures.